Investigations
1st investigations to order
nucleic acid amplification test (NAAT)
Test
Non-invasive sampling (urine or vaginal) is as effective as invasive sampling (vaginal, endocervical, or penile urethral swab) and is more acceptable to patients.[24]
Rectal and oropharyngeal Chlamydia trachomatis infection can be diagnosed by testing at the anatomic site of exposure. There is also good evidence that performance of NAATs on patient self-collected rectal swabs is comparable to clinician-collected rectal swabs, and patients find this self-collection method for chlamydial screening highly acceptable.[18][19]
Sensitivity is high (>90%), as is specificity (94% to 99.5%). NAAT can detect as little as a single strand of DNA to produce a positive result. Chlamydia organisms do not need to be viable in order to obtain a positive result.[17]
If NAAT is negative, but clinical suspicion is high, treat the patient empirically and consider repeat testing.
There is increasing use of near patient rapid NAATs that can provide results within 20 to 90 minutes, depending on the platform used.[25]
Result
positive
Investigations to consider
direct immunofluorescence
Test
Requires an invasive sample (vaginal, endocervical, or penile urethral swab) and is highly specific but less sensitive than NAAT.[26]
Result
positive
enzyme immunoassay
Test
Requires an invasive sample (vaginal, endocervical, or penile urethral swab) and has a sensitivity of about 50% of that of NAAT. The specificity is operator-dependent.[26]
Result
positive
nucleic acid hybridisation tests
Test
Requires invasive sample (vaginal, endocervical, or penile urethral swab).
Result
positive
cell culture
Test
Requires an invasive sample (vaginal, endocervical, or penile urethral swab). High specificity (close to 100%). Sensitivity varies depending on laboratories (70% to 90%).[17] Due to variability and expense, this test is usually only used in cases where legal issues are involved.
Result
positive
Emerging tests
rapid and point-of-care tests
Test
Allow diagnosis and treatment decisions to be made at initial presentation. Potentially decreases onward transmission and complications of infection.
Previously available tests had low accuracy or were expensive to carry out, but there are many point-of-care tests being developed, such as rapid molecular testing for chlamydia, with some evidence that they can improve diagnosis and reduce unnecessary treatment.[20][21][22][23]
Some of these rapid tests are approved by the US Food and Drug Administration.
Result
positive
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